Bias arrangement for depressed collector microwave amplifier tube



Feb. 13, 1968 J. V. STOVER ETAL BIAS ARRANGEMENT FOR DEPRESSED COLLECTOR MICROWAVE AMPLIFIER TUBE Filed Feb. 25, 1965 al Wi Arran/.4%

United States Patent O 3,369,188 BIAS ARRANGEMENT FR DEPRESSED gOLECTUR MICROWAVE AMPLIFIER UB .loe V. Stover and Thomas L. Griffin, Anaheim, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Feb. 25, 19455, Ser. No. 435,306 12 Claims. (Cl. S30-43) This invention relates generally to microwave amplifiers, and more particularly relates to a 'bias arrangement for a linear electron beam microwave amplifier tube operated with a depressed collector potential. As used herein the term bias is intended to mean a D.C. potential applied between any pair of electrodes of an electronic device to establish a desired operating condition.

In microwave amplifiers of the traveling-wave type a stream of electrons traveling from a cathode to a collector electrode is caused to interact with a propagating electromagnetic wave in a manner which amplifies the electromagnetic energy. In order to achieve such interaction the electromagnetic wave is propagated along a slow-wave structure such as a conductive helix wound about the path of the electron stream. The slow-wave structure provides a path of propagation for the electromagnetic wave which is considerably longer than the axial length of the structure, and hence, the traveling wave may be made to effectively propagate at nearly the velocity of the electron stream. Interaction between electrons in the stream and the traveling wave causes velocity modulations and bunching of the stream electrons. The net result may then be a transfer of energy from the electron stream to the wave traveling along the slowwave structure, resulting in amplification of the traveling wave.

In order to increase efiiciency, traveling-wave tubes have been operated with a depressed collector potential, i.e. with the collector electrode biased at a potential significantly lower than the potential of the slow-wave structure. For example, in typical depressed collector operation the collector potential may be in a range essentially from 50% to 70% of the slow-wave structure potential as measured with respect to the cathode.

One prior art arrangement for `biasing a traveling-wave tube for depressed collector operation includes a first power supply connected between the cathode and the collector electrode to maintain the collector at a predetermined positive potential with respect to the cathode. A second power supply, providing a voltage of a magnitude greater than that of the first power supply, is connected between the cathode and the slow-wave structure to bias the slow-wave structure positively with respect to the cathode by the desired amount. In this bias arrangement not only are two power supplies required, but in order to prevent damage to the tube, two rapidly acting high voltage switches also must be employed to disconnect the tube from both power supplies in the event of a fault such as arcing.

In a second prior art biasing circuit for a depressed collector traveling-wave tube a first power supply is again connected between the cathode and the collector electrode to bias the collector positively with respect to the cathode, while a second power supply is connected between the collector electrode and the slow-wave structure to `bias the collector negatively with respect to the slow-wave structure. For the same relative electrode potentials, a lower voltage second power supply may be used in the second arrangement than in the first arrangement. However, both circuits have the same power delivery requirements, and the second arrangement also re- `3,369,188 Patented Feb. 13, 1968 quires two power supplies and two high voltage high speed disconnecting switches.

In a third prior art scheme for biasing a travelingwave tube for depressed collector operation, a first power supply is connected between the cathode and the sloww.ave structure to bias the slow-wave structure positively with respect to the cathode, and a power sink is connected between the slow-wave structure and the collector electrode to maintain the collector electrode at the desired negative potential relative to the slow-wave structure. Although the third arrangement employs only one active power source and only one fast acting high voltage d isconnecting switch, nevertheless, a high current capacity power sink is required. Moreover, the overall power delivery requirements of the third arrangement are significantly higher than those of the first two arrangements.

Accordingly, it is an object of the present invention to provide a bias arrangement for operating a linear electron beam microwave amplifier with a depressed collector potential which requires only one power supply and only one rapidly acting high voltage disconnecting switch, and which bias arrangement also has relatively low power delivery requirements.

It is a further object of the present invention to provide a bias circuit for a depressed collector electron beam microwave amplifier which eliminates the need for one of the power supplies, operated as either a power source or a power sink, heretofore required.

It is a still further object of the present invention to provide a bias arrangement for a depressed collector microwave amplifier tube, preferably of the travelingwave type, which is smaller and lighter than comparable bias arrangement of the prior art.

In accordance with the objects set forth above, the bias circuit of the present invention includes a power supply coupled between the cathode and the interaction structure of the electron beam microwave amplifier to be biased for depressed collector operation and a transformer-rectifier arrangement coupled to the power supply. The primary winding of the transformer is coupled between the interaction stmcture and the collector electrode of the microwave amplifier, while the secondary winding of the transformer and the rectifier are coupled in series across the power supply.

Other and further objects, advantages and characteristic features of the present invention will become readily apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the accompanying drawing in which:

FIG. l is a schematic circuit diagram illustrating one embodiment of the invention; and

FIG. 2 is a schematic circuit diagram showing another embodiment of the invention.

In FIG. l a linear electron beam microwave amplifier tube utilizing a bias arrangement according to the present invention is illustrated as a traveling-wave tube 10 having an electron emitting cathode 12, a slow-Wave interaction structure 14, and a collector electrode 16. An input connection 17 is disposed at one end of the interaction structure 14 to apply incoming microwave energy to the device, while an output Connection 18 is afforded at the opposite end of the interaction structure to facilitate removal of the amplifier microwave energy. A control grid 20 iS interposed between the cathode 12 and the interaction structure 14 in order to control the fiow of the electron stream and thereby facilitate pulsed operation of the travcling-wave tube 10. Although any linear electron beam microwave amplifier tube which it is desired to operate with a depressed collector potential may be employed, by way of example the tube 10 may be a 396H travelingwave tube manufactured by Hughes Aircraft Company, Microwave Tube Division, Los Angeles, California.

In the bias circuit of the present invention a power supply 22, which may be any regulated power supply having appropriate voltage and current ratings, is connected between the cathode 12 and the interaction structure 14, with the positive terminal of the power supply connected to the structure 14 and the negative terminal connected to the cathode 12. The positive terminal of the power supply 22 may also be connected to a level of reference potential designated as ground in FIG. 1. When the aforementioned exemplary traveling-wave tube is employed, a power supply 22 may be selected which provides a D.C. output voltage Ebb of 21.5 kv. at a current of 4.78 amps peak and 47.8 ma. average.

The additional power source or sink required by prior art bias circuits is replaced in the circuit of the .present invention by a transformer-diode arrangement. This arrangement includes a pulse transformer 24 having a primary winding 26 and a secondary winding 28, the phase relationship between signals in the primary winding 26 and the secondary winding 2S being indicated in the conventional manner by the dots adjacent the transformer windings. The primary winding 26 is connected between the collector electrode 16 and ground; while the secondary winding 28 is connected in series with a unidirectionally conductive device, illustrated as a diode rectifier 30, between the negative terminal of the power supply 22 and ground. The diode rectifier 30, which should have a peak inverse voltage rating sufficient to withstand the power supply voltage Ebb, is connected in such polarity that its cathode faces the positive terminal of the power supply 22 while its anode faces the negative power supply terminal. When used with the aforedescribed exemplary travelingwave tube and power supply, the unidirectionally conductive device 30 may be a diode bank comprising 55 units of Hughes HMZG diodes connected in series.

The pulse transformer 24 should provide a large excitation, or open circuit, indnctance in its primary winding 26, and should have an effective ratio of secondary turns Ns to primary turns Np given by:

E ni Ed Where Ebb represents the voltage provided by the power supply 22, Ed represents the voltage across the diode 30 when the diode is conductive, and Ep represents the voltage across the primary winding 26 which is equal to the desired4 voltage between the interaction structure 14 and the collector electrode 16. When the aforedescribed exemplary traveling-Wave tube and power supply are employed, the transformer 24 may be a pulse transformer designed to operate with a primary voltage Eb of 8.5 kv. `at a current of 4.8 amps peak for a pulse duration of 40 microseconds.

in order to permit pulsed operation of the travelingwave tube 1t), a grid modulator 32. may be connected between the control grid and the cathode 12 of the tube 19. The grid modulator 32 may comprise a pulse generator which, for the aforementioned exemplary traveling-wave tube and circuit components, provides at its output terminal connected to the grid 20 a quiescent voltage level of 21.7 kv. with respect to ground and a voltage pulse at a level of 21.1 kv. relative to ground for a duration of 40 microseconds. In the circuit of FIG. 1 the collector current of the traveling-wave tube 11B- (which also flows through the primary winding 26 of the transformer 24) is designated Ic, the current flowing to the interaction structure 14 is denoted Ib, and the current flowing through the secondary winding 28 and the diode 30 is designated IS.

In the operation of the circuit of FIG. 1, assume that initially the grid modulator 32 biases the control grid 20 negatively with respect to the cathode 12 by a sufficient amount (around 20() volts for the aforementioned exemplary traveling-wave tube) to block the flow of electrons. At this time the collector 16 resides at essentially ground potential; and the interaction structure current Ib, the collector current Ic and the transformer secondary current Is are all negligible. The power supply 22 biases the cathode 12 negatively with respect to the interaction structure 14 by an amount Ebb and also establishes a reverse bias across the diode 30.

When the grid modulator 32 provides an output pulse which biases the control grid 20 positively with respect to the cathode 12 by the desired amount (around 400 volts for the aforementioned exemplary traveling-wave tube), electrons leaving the cathode 12 are accelerated toward the interaction structure 14 and the collector 16 by the potential -l-Ebb. Thus, an electron beam is provided along the structure 14, and interaction between microwaves traveling along the structure 14 and the electron beam takes place in the conventional manner to amplify the traveling microwaves. Most of the beam electrons pass through the interaction structure 14 and impinge upon the collector electrode 16, causing a current Ic to flow from the positive terminal of the power supply 22 through the primary winding 26 to the collector 16. Some of the beam electrons are intercepted by the interaction structure 14, and a smaller current Ib iiows from the positive terminal of the power supply 22 to the structure 14.

Since the diode 30 is reverse biased, the current ow through the secondary winding 28 of the transformer 24.1 is negligible, and the secondary winding 28 exhibits an essentially infinite impedance. This high secondary load impedance is reiiected into the primary winding 26 where it appears in shunt with the excitation inductance of the primary winding. Since the primary winding excitation inductance is large, a significant potential drop appears across the primary winding 26 due to the flow of collector current Ib. The potential at the collector electrode 16 is thus reduced to a value substantially below that of the interaction structure 14, thereby facilitating depressed collector operation of the traveling-wave tube 10.

For a transformer 24 designed with a turns ratio according to Equation 1, when the voltage across the primary winding 26 exceeds the design potential Eb, a suicient potential is established acros the secondary winding 28 to forward bias the diode 30. Current flow of a magnitude N l' =A-,1;Ib

thus commences in the secondary winding 2S. The current Is flows in a direction which reduces the net current leaving the power supply 22, thereby conserving power which otherwise would have been dissipated in the power sink if a prior art bias arrangement were employed.

The flow of secondary current Is causes the impedance of the secondary winding 2S to decrease substantially. If the secondary load impedance reflected into the primary winding 26 is sufficiently low to allow the voltage across the primary winding 26 to drop below the design value, the voltage across the secondary winding 28 will decrease suihciently to again reverse bias the diode 30. The flow of secondary current Is ceases, increasing the impedance of the secondary winding 28 to a value suicient to restore the desired design voltage Ep across the primary winding 26. Thus, a substantially constant voltage Eb of a magnitude determined by Equation l is maintained between the interaction structure 14 and the collector electrode 16 so that the collector electrode 16 may be biased to the desired depressed potential. It should be apparent from Equation 1 that vthe constancy of the voltage Eb is a function of the regulation of the power supply voltage Ebb, the forward voltage of the diode 30, and the regulation of the transformer 24.

The depressed collector microwave tube bias arrangemicrowave amplifier having a cathode, an interaction ment illustrated in FIG. 2. is similar to the arrangement structure and a collector electrode comprising: power of FlG. l, and respective components of the circuit o supply means coupled between sai cathode and said FlG. 2 which are the same as those of the circuit of interaction structure for providing a predetermined vo t FIG. l are designated by the same respectve reference 5 age, a transformer having a primary winding and a numerals as their counterpart components. However, in secondary winding, said primary winding being coup e the circuit o l 2 a nongridded traveling-wave tube between said interaction structure and said collector such as a nongridded version of the aforementioned electrode, a diode rectifier device, said diode rectifier de- Hughes 396B traveling-wave tube, is employe A so, vice and said secondary winding being coupled in series in the arrangement o G. 2, a modulator switch tube 1 between said interaction structure and said cathode, sai 34 (which replaces the grid modulator 32 of FlG. l) transformer having an effective ratio of secondary turns is connected between the cathode 12 and the negative NS to primary turns Np given by terminal of the power supply 22. Ns Ebbm Ed As long as the modulator switch 34 is open (nonconf==// ductive) the cathode 12 is eiectively disconnected from 15 D p 'une Power suPPiv 22- Wiien ii is desired to puise the where Ebb represents said predetermined voltage, Ed ireveiinweve tube 1',iiie rnoduieior switch 34 is ciosed represents the voltage across said diode rectifier device for ine desired puise duration io conneci ine negative when said diode rectifier device is conductive, and p terrninei oi ine Power suPPiY 22 io 'die cathode il An represents the desired voltage across said primary windelectron beam is thus caused to flow from the cathode 'mg during Operation ci Said microwave amplifier, 11 io 'die coiiecior 1o, resuiiing in the desired opere' 4. A circuit for biasing a linear electron beam microiiOn 0i ine irnveiing'weve tube and iis biasing circuiirv wave amplifier having a cathode, an interaction structure in ine seine rnenner es discussed above with respect io and a collector electrode for depressed collector opera- FlG. l. tion comprising: a power supply for providing a pre- FrOIn the foregoing, ii wiii be ePPareni 'diei 'die circui'rs 25 determined voltage between first and second terminals 0f FGS- i 'and 2 Provide sirnPie and cornPnci bias adapted to be connected directly to said interaction strucarrangements for depressed coiiecior rnicroweve iubes ture' and said cathode, respectively; a transformer having which afford substantial cost savings due to the eliminaa primary winding connected directly between Said col. tion oi one Power suPPiv and one disconnecting swiicii lector electrode and said interaction structure and having rorn Prior eri errengernenis- Moreover, eddiiionei cosi a secondary winding; and a unidirectionally conductivf savings nre reeiiZed es e resuit oi Power conservation device, said unidirectionally conductive device and sail during opererion of 'die circuiis or 'die inveniionsecondary winding being connected in series between sai lt should also be apparent that while the present infirst and Second terminals, vention has been illustrated and described with specific 5 A circuit icr biasing a linear electron beam mici-i reference to pulse modulated traveling-wave tubes, bias wave amplifier having a cathode, a control electrod nrrnngernenis according io ihe invention rnav be ernan interaction structure and a collector electrode for Pioved in conlunciion with env iineer eieciron benin pressed collector operation comprising'. a power supp rnicroweve nInPiiier opereiing with n depressed coiieeior coupled between said cathode and sa'd interaction stri potential. ln addition, although the transformer 24 has tnre, a transformer having a primary wind'ng an been described as a pulse transformer, an audio trans- 40 Secondary winding,` said primary winding bei g coup orrner wouid be used ir the tube 10 is io be nrnPiiiude between said interaction structure and said collector e Inodninied at Voice frequencies; 0r die irnnsrorrner 24 trode, a unidirectionally conductive device, said un could be replaced with a D.C.to-D.C. converter if the rccticnally conductive device an sai secondary wi tube were operated on a continuous wave basis ing being coupled in series between sa'd interaction st Thus, eiiiiougn irre invention uns i)een shown rnd 45 ture and said cathode, and means for applying a cor described with reference to particular embodiments, signal between said control electrode and said catho various changes and modifications obvious to a person 6, A circuit or biasing a linear electron beam m skilled in the art to which the invention pertains are wave amplifier having a cathode, an interaction strui deemed 't0 lie Within 'die purview O die invention. and a collector electrode for depressed collector o What is claimed is'. 50 tion comprising: a power supply for providing a 1- A bias arrangement or a linear electron benin determined voltage between first and second term microwave amplifier having a cathode, an interaction said first terminal being coupled to said interaction structure and a collector electrode comprising` a power ture, a transformer having a primary winding i supply coupled between said cathode and said interaction Secondary winding, said primary winding being c( siruciure, e irensiorrner having n Primary Winding and a between said interaction structure and said collecto secondary winding, said primary winding being coupled trode, a unidirectionally conductive device, said between said interaction structure and said collector elecrectionally conductive device and said secondary u trode, and a unidirectionally conductive device, said unibeing coupled in series between Said St and directionally conductive device and said secondary windterminals, and a modulator switch tube coupled i ing being couPied in series across seid Power suPPivsaid cathode and said second termina 2. A bias arrangement for a linear electron beam 7. Abias arrangement for atraveling-wave tube microwave amplifier having a cathode, an interaction a cathode, a slow-wave structure and a collector e structure and a collector electrode comprising: power comprising: a. power supply coupled between said supply means for providing a predetermined voltage beand said slow-wave structure, a transformer tween first and second terminals, the positive terminal primary winding and a secondary winding, said being coupled to said interaction structure and the negawinding being coupled between said slow-wave tive terminal being coupled to said cathode, a transand said collector electrode, and a unidirection former having a primary winding and a secondary windductive device, said unidirectionally conductii ing, said primary winding being coupled between said and said secondary winding being coupled in ser interaction structure and said collector electrode, and a said power supply.

diode rectifier coupled in series with said secondary wind- 8. A bias arrangement for a traveling-wave ing between said terminals in a manner to provide uniing a cathode, a slow-wave structure and a colli directional current dow through said secondary winding trode comprising: power supply means or p in a direction toward the positive terminal. predetermined voltage between first and second 3. A bias arrangement for a linear electron beam the positive terminal being coupled to said structure and the negative terminal being coupled to said ture and the negative terminal being connected to said cathode a pulse transformer having a primary windinU cathode, means for applying a control pulse between said an a secondary wi ding said primary winding having a control grid and said cathode a pulse transformer having arge excitation inductance and being coupled between a primary winding and a secondary winding, said primary said s ow-wave structure and said collector electrode a winding having a large excitation inductance and being diode rectifier device couple in series with said second connected between said slow-wave structure and said colary winding between said terminals in a manner to prolector electrode, a diode rectifier device having an anode vide unidirectional current fiow through said secondary terminal and a cathode terminal said diode rectifier de winding in a direction toward the positive terminal said vice and said secondary winding being connected in series transformer having an effective ratio of secondary turns i0 between said first and second terminals with said cathode s to primary turns i, given by terminal facing e positive one of said first and second terminals, said transformer having an effective ratio of i:Ebb`i`Ed secondary turns Ns to primary turns Ni, given 'by ND ED i`E'bb+Ed where Ebb represents said predetermined voltage, Ed rep- Np` E resents the voltage across said diode rectifier device when Where Ebb represente Said predetermined Vonage, Ed rcpsaid diode ieeiiiief device is eoiidiietive ami. i repre resents the voltage across said diode rectifier device when ,Seiits the C iesiiei Voiiage aeross Said Primary Winding dbf' said diode rectifier device is conductive and represents ine operation'of saidtraveling-Wave t b 20 t e desired depressed collector voltage across said primary A eiieiiit for biasing a iiiiveiiiig'waie iiibe iiaViiig i winding during operation of said traveling-wave tube.

cathode, a control electrode, a slow-wave structure and a circuit or binsing a naveiingweve tube havin(7 coiiecibi eieeiioiie fbi depressed eoiieeibi OPeiiiiOii 'com' a cathode, a slow-wave structure and a collector electrode prising': a power Supply COHHeCed between Said Cathode or depressed collector operation comprising. power su andhsaid slow-wave structure, a pulse transformer hai/ing ply means for providing a predetermined voltage between a primary Winding and a Secondary Winding Said Piiiiiaiy rst and second terminals, t e positive terminal bein Winding being Connected between Said ibWWaVe Siiiietiife connected to said slow-wave structure and the negative and said collector electrode, a unidirectionally conductive erininai being connected tc Seid cathode, n puise Open device, said unidirectionally conductive device and said ated Switch tu e connected between Seid cathode and the secondary winding being connected in series between said Winding, said primary winding having a large excitation aid cath inductance and being connected between said slow-wave 10' A Circuit for biasing a iiaveiiiigwave tube bai/ing structure and said collector electrode, a diode rectifier cathode, a slow-wave structure and a collector electrode device having an anode terminal and a cathode terminal, ir depressed collector operation comprising: a ower lPPlY fOr Providing predetermined foliage .between ing connected in series between said first and second ternii- 'st and second terminals, said first terminal lbeing connals with said cathode terminal facing the positive one cted to said slow-wave structure, a pulse transformer ing an effective ratio of secondary turns Ns o primary mary winding being connected between said first termimins p giVen by and said collector electrode, a unidirectionally conducl evice, said unidirectionally conductive device and Limi l secondary winding being connected in series between Nn En and a pulse operated where Ebb represents said predetermined voltage, Ed repch tube connected between said cathode nd said secresents the voltage across said diode rectifier device when terminal. said diode rectifier device is conductive, and Ei, represents i A circuit for biasing a traveling-wave tube havin the desired depressed Collector voltage across said primary ode, a control grid a slow-wave Structure and a winding uring operation of said traveling-wave tube.

ctor electrode for depressed collector operation comig: power supply means for providing a predeter- No references cited.

ve terminal being connected to said slow-wave struc- SAXFIELD CHATMON, IR Pff/71H13 Examiner 

1. A BIAS ARRANGEMENT FOR A LINEAR ELECTRON BEAM MICROWAVE AMPLIFIER HAVING A CATHODE, AN INTERACTION STRUCTURE AND A COLLECTOR ELECTRODE COMPRISING: A POWER SUPPLY COUPLED BETWEEN SAID CATHODE AND SAID INTERACTION STRUCTURE, A TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING, SAID PRIMARY WINDING BEING COUPLED BETWEEN SAID INTERACTION STRUCTURE AND SAID COLLECTOR ELECTRODE, AND A UNIDIRECTIONALLY CONDUCTIVE DEVICE, SAID UNIDIRECTIONALLY CONDUCTIVE DEVICE AND SAID SECONDARY WINDING BEING COUPLED IN SERIES ACROSS SAID POWER SUPPLY. 